Polysiloxanes and organosilicone copolymers find use in diverse fields of application, as, for example, additives to paints, varnishes, adhesives, and cosmetics, in textiles finishing, in plastics processing, or in papermaking and textile production.
Organosilicone copolymers are obtained, for example, by free-radical polymerization in organic solvents or in aqueous dispersion by emulsion polymerization or suspension polymerization. Owing to the poor compatibility of the reactants, particularly at a silicone fraction of more than 25% by weight, the polymerization during the preparation of organosilicone copolymers from olefinic monomers and silicones is accompanied by problems due to phase separation or gelling, which leads to hazing of the organosilicone copolymers. These problems occur particularly when the solids content is increased during the polymerization.
The free-radical solution polymerization is described, for example, in DE 4240108 A1, using toluene, xylene, and butyl acetate as solvents. In the course of the polymerization of free-radically polymerizable monomers, polysiloxane is embedded into a polymer matrix. The crosslinking of the polymer matrix and of the polysiloxanes takes place only following addition of a further component, at the application stage. Prior to crosslinking, there may be gelling and phase separation of the organosilicone copolymer components.
WO 03/085035 A1 describes a process of free-radical solution polymerization which uses solvent mixtures comprising at least two nonaqueous solvents. Also described are solutions of high silicone content organosilicone copolymers with a high solids content. This was achieved through the use of very specific solvent mixtures. However, all of the polymer compositions disclosed specifically with a solids content above 30% exhibit phase separation, gelling and/or crosslinking. Furthermore, the use of solvent mixtures is a disadvantage in terms of process engineering, since the solvent mixtures require distillative separation—which is costly and inconvenient—in order to allow the individual solvent components to be recycled.
Against this background, the object is to provide highly transparent, high silicone content organosilicone copolymers in the form of their high solids content solution, and an economically efficient process for their preparation.